An internal combustion engine with a supercharger has been developed with improved charging efficiency obtained by means of utilizing kinetic effects, such as inertia effects or resonance effects, of intake air. To obtain high volumetric efficiency over a wide range of engine speeds, it was taught that the natural frequency of resonance air column should be changed depending upon engine speed. One example of such internal combustion engines is disclosed in, for example, Japanese Patent Publication No. 60-14,169, consisting of cylinders divided into two groups, so that adjoining cylinders in each group do not fire one after the other. The cylinders in each group are separately communicated with an intake collecting passage by way of discrete intake passages. The intake collecting passages for the two groups of cylinders are communicated with each other by way of separate intake resonance passages having enlarged volume chambers, such as surge tanks, respectively. A switch means is disposed at the junction of the intake resonance passages for the two groups of cylinders for bringing the intake resonance passages into communication with each other in high engine speed range or interrupting communication therebetween in low engine speed range.
According to the internal combustion engine, the vibration of an air column in the intake resonance passage is generated by pressure waves due to periodic openings of the intake ports of the cylinders, generating the vibration of the air column in the intake collecting passage and the discrete intake passages. The resonance of vibration of the air column induces the greatest amplitude of pressure vibration, thereby greatly enhancing resonance effect of supercharging. The resonance effect supercharging is still more improved or enhanced by forming the intake resonance pipe with no enlarged volume chamber wherein pressure vibrations are attenuated. The provision of the intake resonance pipe having no enlarged volume chamber also contributes to an attempt at making the intake system, and hence the engine, compact.
In the above mentioned internal combustion engine, the more downstream a cylinder is located, the lesser the amount of intake air fed to the cylinder is with respect to an upstream located cylinder, whereby intake air is possibly unequally distributed and supplied among the cylinders. That is, when a cylinder is in its intake stroke in the state or condition that the intake air is less dense in the intake resonance pipe immediately after the intake of a cylinder located upstream the cylinder, the amount of intake air supplied to the downstream located cylinder tends to become less. The more the tendency is strengthened, the smaller the diameter of the intake resonance pipe becomes. However, in the case of supercharging intake air by way of utilizing kinetic effects, such as resonance effects, increasing the diameter of the intake resonance pipe results in a small amplitude of pressure vibration and weakened supercharging effect.
To obtain high engine output, it was thought that the intake system which charging air to the engine with utilizing resonance effects of intake air should be provided with a supercharger. If volumetric efficiency is not uniform among the cylinders, a cylinder having a volumetric efficiency higher than that of the other cylinders is apt to knock. In order to avoid knockings, it is required to decrease supercharging pressure, to retard firing timings or to change the compression ratio of intake air. This leads to an insufficient engine power output and an decrease of fuel efficiency.